1. Field of the Invention
This invention relates generally to a system and method for determining the center of gravity height and mass of a vehicle for roll control and, more particularly, to a system and method for determining the center of gravity height and mass of a vehicle for roll control that includes providing frequency analysis of measured or estimated vehicle states using a vehicle dynamic model.
2. Discussion of the Related Art
Vehicle roll over control has become an important issue with the increased popularity of high center of gravity (CG) vehicles, such as sport utility vehicles (SUVs). In vehicle roll over and roll motion, the vehicle CG height and mass are critical parameters. Vehicle roll over warning and mitigation systems would thus benefit from accurate knowledge of vehicle CG height and mass.
It is known in the art to prevent potential vehicle rollover using, for example, differential braking control, rear-wheel steering control, front-wheel steering control, or any combination thereof. A vehicle roll estimation system may receive vehicle dynamics information from various sensors, such as yaw rate sensors, lateral acceleration sensors and roll rate sensors, to determine the proper amount of action to be taken to detect a potential vehicle rollover condition. A balance typically needs to be provided between estimating the vehicle roll motion and the vehicle yaw motion to provide the optimal vehicle response. Thus, it is usually necessary to detect certain vehicle conditions to provide the roll detection.
Vehicle roll stability information can be provided to vehicle drivers or impending vehicle rollover can be mitigated by activating adequate chassis control systems with knowledge of vehicle roll stability conditions. Vehicle rollover warning or avoidance systems, therefore, will show satisfactory performance if the roll stability conditions are actively known to the systems. To precisely identify vehicle roll stability conditions, it is advantageous to know the vehicle's roll rate and roll angle since they are the most important states in vehicle roll dynamics.
Nominal values of vehicle CG height and mass can be measured and employed in rollover mitigation systems. However, actual values of vehicle CG height and mass vary as a result of vehicle loading conditions, such as passengers. Truck-based vehicles, SUVs and pick-up trucks, usually have large load capacities and consequently have large variations in CG height and mass.
U.S. Patent Application Ser. No. 11/563,251, filed Nov. 27, 2006, titled In-vehicle Identification of the Relative CG Height, assigned to the assignee of this application, and herein incorporated by reference, discloses one method for identifying vehicle CG height. However, this technique does not identify vehicle mass even though both vehicle CG height and mass are important in vehicle roll motion. In addition, because this technique employs multiple Kalman filters simultaneously, it requires high computational power, which may not always be available for real-time application in production vehicles.